As an electronic controller that: is placed in a severe environment (in terms of mountability, heat resistance, oil resistance, etc.) in which an engine room, a transmission, etc. are used; and controls an engine, an automatic transmission, and the like for example, an electronic controller having such a structure as shown in, for example, JP-A-2004-119465 or JP-A-2006-86296 is disclosed. (JP-A-2004-119465 is also published as a patent document US2004-084756)
An electronic controller shown in JP-A-2004-119465: comprises a circuit board on a surface (the top surface) of which elements (circuit elements) are mounted and, on the other surface (the bottom surface) thereof, thick film resistors (printed resistors) as other elements are formed, a base member (a base) to which the circuit board is bonded using the surface on which the thick film resistors are formed as the bonded surface, and members other than the base member; and is provided with external connecting terminals (lead terminals) electrically connected to the base member. Further, except parts of flanges formed in the base member in order to fix the electronic controller and release heat and parts of the external connecting terminals, the circuit board, the base member, the external connecting terminals, and the flanges are molded in a lump with sealing resin (molding resin).
An electronic controller shown in JP-A-2006-86296 has a circuit board on a surface (the bottom surface) of which, the surface being bonded to a base member (a radiator plate), thick film resistors as elements and all the electronic components (including bare chips (semiconductor chips)) mounted not by soldering are mounted by the method of flip chip for example and, on the other surface (the top surface) thereof, all the electronic components (including microcomputers (IC chips)) including chip resistors as other elements are mounted by soldering. Further, a recess (a first concave portion) is formed at the position corresponding to the electronic components mounted on the circuit board on the surface of the base member to which the circuit board is bonded. Furthermore, the electronic controller is molded with sealing resin (resin) in the state where parts of external connecting terminals (electrodes for external connection) and a part of the base are exposed to exterior.
In the configuration shown in JP-A-2004-119465, the area of the thick film resistors on the bottom surface of the circuit board is not identical to the area of the elements on the top surface of the circuit board, the board size is restricted by the area of either of the surfaces, and that is an obstacle to the efficient downsizing of the board. More specifically, the area where the thick film resistors are formed on the bottom surface is smaller than the area where the elements are mounted on the top surface. Consequently, the area of the circuit board is restricted by the top surface of the board and a useless space appears on the surface on which the thick film resistors are formed. That is not desirable from the viewpoint of mountability (downsizing) and heat dissipativity.
Further, with regard to the elements mounted on the top surface of the circuit board, soldered elements and non-soldered elements (for example, bare chips bonded and fixed with an electrically conductive adhesive and connected with wire) coexist. Hence, in order to avoid defective bond at the wire connection of elements caused by solder spattering or flux residues after the mounting by soldering, it is necessary to: stick a masking tape to a site to which wire is connected when an element is mounted by soldering; peel off the masking tape after the mounting; and further apply wet cleaning or plasma cleaning. Meanwhile, when soldering is applied in advance, since the surface of the board on which elements are already mounted is not flat, successively an electrically conductive adhesive cannot be supplied at one time by printing, thus the adhesive must be supplied one spot by one spot with a dispenser or the like, and productivity deteriorates considerably. The coexistence of such soldered elements and non-soldered elements on a same plane as stated above makes processes very complicated.
Meanwhile, when an electronic controller is mounted on a place where the temperature environment is very severe, such as mounted directly on an engine or incorporated into a transmission, cracking and exfoliation of sealing resin must be particularly taken into consideration. As a mold size increases, thermal strain increases and cracking and exfoliation of sealing resin tend to occur. In JP-A-2004-119465 however, the downsizing of a circuit board is limited as stated above and hence it is configured so that a base member (except flange portions) may not be exposed from sealing resin in order to prevent the cracking and exfoliation of the sealing resin. Consequently, it is not desirable from the viewpoint of heat dissipativity.
In contrast, in the configuration shown in JP-A-2006-86296, electronic components, in addition to the thick film resistors, are mounted on the bottom surface of the circuit board and a first concave portion is formed at the position of the base member corresponding to the electronic components. Consequently, the circuit board and the electronic controller can be downsized in comparison with the configuration shown in JP-A-2004-119465. Further, electronic components attached not by soldering are mounted on the bottom surface of the circuit board and electronic components attached by soldering are mounted on the top surface thereof. It is possible therefore to simplify the mounting processes without the complication of the processes caused by the coexistence of the mounting by soldering and non-soldering. Furthermore, since a part of the base member is exposed from the sealing resin, heat dissipativity can be improved in comparison with the configuration shown in JP-A-2004-119465.
In JP-A-2006-86296 however, it is configured so that semiconductor chips are mounted in the state of bare chips on the bottom surface of the circuit board by the method of flip chip. Consequently, the dimensional accuracy of electrodes (lands) and accuracy of distance between electrodes on the circuit board connected to bumps are severe, further warpage occurs in the board due to heat at the forming of the circuit board or the like (for example, baking at the forming of a ceramic substrate, or the like), and hence it is likely to deteriorate the reliability in connection between elements and the circuit board. Here, when elements are connected with wire on the bottom surface of the circuit board, in the event of bonding and fixing the circuit board to the base member, it is likely to get pressure and break wire and deteriorate the reliability in connection between elements and the circuit board. In addition, the size of the first concave portion (gap between the circuit board and the base member) increases to the extent corresponding to the wire and hence it is not desirable from the viewpoint of heat dissipativity.